Have used these for 3+ years and 100+ nites out with no issues... great filter... Comes with a backflush fitting too, nice to have for clean out at home...Inexpensive at about $25, too.

Put a positive check valve in the line and you can use your hydrator as a gravity system in camp...very nice and convient feature...Also with the PCV you can eliminate the bite piece and just use the end like a straw after the PCV, that is.... another gram saved.

A minor word of caution on the Seychelle which may or may not be a concern for others.

The Seychelle is what is known as a Cyst filter. It will remove Giardia and possibly some/most Crypto, but won't remove bacteria or viruses. Even some Crypto can get through because of its "flexible" nature and its ability to fold over on itself (not the norm, but it does happen.), thus effectively making all of its dimensions small enough to pass through the pores of the Seychelle. I have personally seen this phenomenon under a microscope decades ago.

Also, keep in mine, and this is my opinion only, that based upon first-hand examination of the Seychelle, i believe that it might be damaged (i.e., cracked) if used in below freezing conditions as any water left in its pores will freeze and expand, thus possibly cracking what appears to be a relatively inelastic filter element.

-------------JT, would like to learn something from you if you don't mind teaching. You mentioned an in-line check valve (i know what check valves are, what purpose they serve, and how they function). Can you please explain why you feel one is necessary for gravity filtration? I'm wondering why water would flow backwards when used in gravity filter mode. I can't picture in my mind the precise scenario that you are envisioning that would make a check valve an important component. I'm NOT saying you're idea is bad, i just can't picture it. Many thanks in advance for your time and knowledge. -- pj

In Ryan Jordan's book LIGHTWEIGHT ... he describes a gravity system using a Platypus reservoir or ZIP and then an inline Sweetwater Siltstopper and then an in-line Seychelle filter while using chlorine dioxide in the Platypus before filtering. They also mentioned that this might be a little overkill.

This seems to work BUT does anyone have a good way of hanging a 2 liter Platypus filled with water?

Given that this filter does not "fold' I'm not sure that I understand your caution... I know that it does not filter viruses...none of the filters do that...you need a purifier to eliminate the virile threat....

As a filter it is advertised to the same micro level of effectiveness as most filters.

To the issue of a positive check or flow valve....These are convienent water saving devices made by Camelback (and probably others, but I never looked further)... Recognizing that you understand these items. this is my take on them... Using one eliminates bite valve drip on old valves.... it eliminates embarassing puddles and wet sleeping bags nearby in crowded shelters when someone kneels on a bite valve (normally not their own) BTW, I have seen this on at least three occasions while eating at the table in front of such a shelter...Finally if you hang the bladder, filter in line, the valve becomes a convenient on-off faucet on a gravity filtration system...Saves lots of time in camp as other chores can be done while the pot or bottle fills...plus at this point you really no longer need the bite valve/end sack... (although I would agree that the bite valve/cover helps keep any dirt out)...yes, you could take the bladder down or raise the end above the bladded to end the flow... but then you have to relocate the bladder or secure the end to the higher point...I just find it convient to establish the water point, hang it at a level that works for my pot/cup and simply turn it off or on as needed without further adjustments...Also I don't have to squeeze the valve as so many other do, or alternatively, remove the bite valve for the gravity flow... which necessitates putting it some where and remembering to reattach later...

As a side note.... My Camel back bite valve weighs 3.5 grams....My Camelback positive on-off valve weighs 3.5 grams....So, one can have all this security and convience without weight penalty by simply swapping out the bite valve for the pos on-off valve...Any way, It works for me.

Msr Dromedary Bag: when I travelled with a group of four, we had a 2.5 gallon dromedary bag we would fill when we stopped to camp. it has webbing around its perimiter and is easy to hang. the output of the filters could be filtered directly into pots, drinking bottles or into a drinking bladder.

I have read that people use stuffsacs to hold the upper bag (some have a strap across the bottome of the bag which can be used.

The safe water any where bags had there own handle.

Camelbacks have a hande which can, with some effort be made to hang the bag with the drain down.

Some things are so obvious but easy to overlook. I put in a check valve because i wanted the angle, i never thought about taking the bite tube off which is a aggrevation.

I understand now what your are referring to. When you said "check valve" i was picturing a valve designed solely to prevent backflow in a fashion similar to what is used in some larger hydraulic systems, e.g., some submarine nuclear reactor systems. These you don't turn on and off. They operate automagically to prevent backflow and do nothing to prevent flow in the normal/forward direction. Hence my confusion. Thanks again for the explanation.

As far as the filter. By 'fold' i was referring to the Crypto 'spore', not the filter.

As for pore size, check even the BPL on-line store. It's a 2micron pore size, not a 0.2micron pore size. Hence, most bacteria will pass, including E. coli, which is an indicator of fecal contamination and only rarely are certain strains/sero-types considered pathogens, as well as many true human pathogens will pass through the filter as well. However, in most cases, hikers are NOT as concerned about bacteria in backcountry water sources as they are about spores/cysts.

As far as 'spores' go, the BPL store's webpage is largely correct. Most Crypto will be filtered out, but there is an uncommon (i hesitate to use the word rare in this case) occurence with Crypto spores where they will fold over on themselves and thus be less than 2microns in any dimension. As i said, i have observed this myself viewing C. parvum under a microscope several decades ago. These may pass through the Seychelle filter purely from a size/geometry standpoint. The Seychelle appears to be a labyrinth type of mechanical barrier filter, so this, IMHO, will reduce the likelihood of this happening, but it simply can't be ruled out, IMHO.

How bad is C. parvum? Varies by the person and the strain - some more virulent than others. BTW, it's estimated based upon samplings taken from various geographical areas that 85% of the NA population has been exposed to Crypto at some time in their life. I think most people are more concerned about Giardia than Crypto, particularly Thru-Hikers (due to the onset of each after ingestion - Crypto typically about a week, but can be as short as a couple of days [the virulence of Crypto varies widely as well as some people's tolerance for it] or longer in some cases; Giardia is typically 1-2weeks). My point here is that many hikers will be home before they experience the symptoms of Giardia (that's NOT to say that this is 'ok', only better - relatively speaking - personally, i'd rather be near the porcelin altar than out on the trail), whereas in some cases Crypto may hit the short-Trek hiker while still on the trail. Also, i believe in most cases Giardia may produce a worse effect. My wife and i have both had Giardiasis - many yrs ago. Fortunately, we were both home by the time the symptoms appeared. Unfortunately, from my wife's perspective, she had it worse; though mine was no pleasant experience by any means either.

I hope that this clears up what i was trying to say in my prev. Post. Sorry, i wasn't clearer there.

Thanks again for your reply and detailed description of the 'check valve' and gravity filter. Makes sense to me now.